"Drainage layers" of coarse material causes excess water, which defies gravity and remains in grow media, to "perch" (like a bird) above the drainage layer, never a good thing. Strata of saturated soil in a pot limits root function and causes the cyclic death and regeneration of the fine roots which do all of the plant's heavy lifting. When fine roots die, the plant's chemical messengers signal the plant to stop top growth until the volume of roots is sufficient to support additional top growth. Even if you don't SEE it, excess water in the pot is a pernicious robber of the plant's potential. What happens is illustrated in the image I provided above, which also illustrates the contrast between how large objects (as opposed to drainage layers) affect how much excess water a planting can have.
If a medium supports excess water between soil particles, the excess changes location from the pot bottom (when no "drainage layer" exists), to immediately above the drainage layer when one is in place. Grower's would be much better served using large objects as ballast, which displaces soil capable of holding excess water, than using a drainage layer which does not change water retention. It simply changes where the excess water is located in the pot.
Al
